$re = '/(\w+)\s*:\s*((?:(?!\s*\w+\s*:).)*)/m';
$str = 'field1 : value1a value1b
field1 : value1a value1b field2 : value2a value2b
field1 : value1a field2 : value2a value2b field3 : value3a value3b value3c';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php